[CELL] allow linux to map Cell regs on legacy SLOF tree.

[CELL] allow linux to map Cell regs on legacy SLOF tree.

The platforms missing the "cpus" property in the "be" node are mono-Cell
platforms such as CAB or Getaway.

Therefore it is possible to assume that if there is no "cpus" properties
under the "be" node then we can safely return the "device node" without
more checking. This is a bit hacky but ... it allows it to work on
these platforms.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
Acked-by: Christian Krafft <krafft@de.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>